The “Digital Enhanced Cordless Telecommunications” system (DECT) is standardized by the European Telecommunications Standards Institute and is an example of a system that uses TDMA-TDD (Time Division Multiple Access—Time Division Duplex) for radio communication. In DECT, transmission is synchronized between all base stations, i.e. all downlink transmission occurs during a first 5 ms period of a frame and all uplink transmission occurs during a second 5 ms period of the same frame. On one TDMA-TDD carrier frequency the first 5 ms period is dedicated to 12 downlink time slots and the second 5 ms period is dedicated to 12 uplink time slots, enabling the use of one single carrier frequency for both downlink and uplink communication of the same bi-directional connection.
Known TDMA-FDD (Time Division Multiple Access—Frequency Division Duplex) systems separate downlink transmission from uplink reception by performing the two tasks on different carrier frequencies and at different times in the mobile radio stations, but simultaneously in the radio base stations. The GSM and D-AMPS systems are examples of TDMA-FDD systems.
TDMA-TDD and TDMA-FDD systems both have their advantages and disadvantages. WO 97/21287 (ADVANCED MICRO DEVICES) describes a system that attempts to combine the advantages of TDMA-TDD and TDMA-FDD. In this combined TDMA-TDD/FDD system the uplink and downlink transmission between a radio base station (BS) and a mobile radio station (MS) are separated both in time and frequency. The uplink and downlink transmissions use separate frequency bands, as in TDMA-FDD, but uplink and downlink transmissions also use separate time intervals, as in TDMA-TDD. However, a disadvantage of the system described in WO 97/21287 is that, by transferring the uplink transmission to a frequency band that is separate from the downlink transmission band, each band will only be used 50% of the time, which is a significant waste of valuable spectrum resources.